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Specific Gravity Test identification and geology

Specific gravity SG measures the ratio of a mineral's density to the density of water 1 g/cm³ at 4°C . It quantifies how heavy a mineral feels relative to its volume and is one of the most powerful diagnostic properties because it is determined by both chemical composition and crystal packing. Metallic ore minerals tend to have high SG values galena 7.6, gold 19.3 , while most silicates fall in the 2.5–3.5 range, and some evaporite or organic minerals can be below 2.0. The standard laboratory method uses a beam balance and Archimedes' principle. The mineral is weighed in air and then submerged in water; the difference in weight equals the weight of water displaced, and SG = weight in air ÷ weight in air − weight in water . Heavy liquids bromoform, methylene iodide, sodium polytungstate solutions provide a rapid qualitative estimate by observing whether the mineral sinks or floats in liquids of known density. In the field, SG estimation is often done by hefting—experienced geologists develop an intuitive feel for density by repeatedly handling known minerals. This qualitative method is surprisingly effective for distinguishing between minerals of very different densities e.g., barite SG 4.5 vs. similar-looking calcite SG 2.7 , though it is unreliable for closely spaced values. Tips: Ensure the specimen is free of air bubbles when submerged—tap gently or use a wetting agent. Avoid porous or heavily fractured specimens; they trap air and give falsely low SG values. For very small specimens, use a hydrostatic balance designed for gemological work. The hefting method works well with practice—always heft a known reference mineral quartz or calcite alongside the unknown for comparison. Heavy liquids require proper ventilation and PPE; sodium polytungstate is much safer than bromoform or methylene iodide but still requires gloves and eye protection.. Equipment: Laboratory method: analytical balance 0.01 g precision , beaker of distilled water, thin wire or thread, suspension apparatus. Field method: spring scale or hand-held digital scale, graduated cylinder, overflow can. Heavy liquid method: sodium polytungstate solution non-toxic alternative to bromoform , glass separation funnel, safety glasses, gloves. Procedure: 1. LABORATORY Archimedes METHOD: a. Weigh the dry mineral specimen in air W air . Record to 0.01 g. b. Fill a beaker with distilled water at room temp

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:00:37.048321+00:00
Review status
Published; not independently peer-reviewed
  • How Do Geologists Identify Minerals? — Utah Geological Survey. Practical guidance on diagnostic physical properties and identification tests.
  • Mineral ID Key — Mineralogical Society of America. Detailed test methods, repeatability guidance, and safety cautions.

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Common questions

What is the Specific Gravity Test used for?
Specific gravity SG measures the ratio of a mineral's density to the density of water 1 g/cm³ at 4°C . It quantifies how heavy a mineral feels relative to its volume and is one of the most powerful diagnostic properties because it is determined by both chemical composition and crystal packing. Metallic ore minerals tend to have high SG values galena 7.6, gold 19.3 , while most silicates fall in the 2.5–3.5 range, and some evaporite or organic minerals can be below 2.0. The standard laboratory method uses a beam balance and Archimedes' principle. The mineral is weighed in air and then submerged in water; the difference in weight equals the weight of water displaced, and SG = weight in air ÷ weight in air − weight in water . Heavy liquids bromoform, methylene iodide, sodium polytungstate solutions provide a rapid qualitative estimate by observing whether the mineral sinks or floats in liquids of known density. In the field, SG estimation is often done by hefting—experienced geologists develop an intuitive feel for density by repeatedly handling known minerals. This qualitative method is surprisingly effective for distinguishing between minerals of very different densities e.g., barite SG 4.5 vs. similar-looking calcite SG 2.7 , though it is unreliable for closely spaced values.
How do you perform the Specific Gravity Test?
1. LABORATORY Archimedes METHOD: a. Weigh the dry mineral specimen in air W air . Record to 0.01 g. b. Fill a beaker with distilled water at room temperature. c. Suspend the specimen from a thin wire attached to the balance so it is fully submerged and not touching the sides or bottom. d. Record the apparent weight while submerged W water . e. Calculate SG = W air / W air - W water . 2. FIELD displacement METHOD: a. Weigh the specimen on a portable scale W air . b. Fill a graduated cylinder with water and record the initial volume V1 . c. Gently lower the specimen into the cylinder. d. Record the new volume V2 . The displaced volume = V2 - V1 in mL = cm³ . e. Calculate SG = W air in grams / displaced volume in cm³ . 3. HEAVY LIQUID METHOD: a. Prepare sodium polytungstate solutions at target densities e.g., 2.67, 2.89, 3.32 g/cm³ . b. Drop the mineral into the solution. Observe: sinks SG liquid , floats SG < liquid , or hovers SG ≈ liquid . c. Test in progressively denser or lighter liquids to bracket the SG.
How do you interpret the Specific Gravity Test?
SG < 2.0: rare; halite 2.17 , sulfur 2.07 , some zeolites, amber 1.08 . SG 2.5–3.0: most common silicates quartz 2.65, feldspars 2.55–2.76, calcite 2.71 . SG 3.0–4.0: many darker silicates, fluorite 3.18 , apatite 3.1–3.35 . SG 4.0–5.0: barite 4.48 , zircon 4.6–4.7 , many oxides. SG 5.0–8.0: most metallic sulfides and oxides pyrite 5.0, galena 7.58 . SG 8.0: native metals, platinum group minerals. Porous, fractured, or inclusion-rich specimens will yield inaccurate results; use clean, solid fragments.
What equipment is needed for the Specific Gravity Test?
Laboratory method: analytical balance 0.01 g precision , beaker of distilled water, thin wire or thread, suspension apparatus. Field method: spring scale or hand-held digital scale, graduated cylinder, overflow can. Heavy liquid method: sodium polytungstate solution non-toxic alternative to bromoform , glass separation funnel, safety glasses, gloves
What safety precautions apply to the Specific Gravity Test?
The listed safety level is caution.

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